Metal films are used widely within semiconductor integrated circuits to make contact to and between semiconductor devices (i.e., metal interconnects). Because of the high densities required for modern integrated circuits, the lateral dimensions of interconnects, as well as the lateral dimensions between interconnects, have shrunk to such a level that a single defect can destroy an entire wafer die by shorting a junction region or open-circuiting a gate electrode of an essential semiconductor device. Defect reduction within interconnect metal films, therefore, is an ever-present goal of the semiconductor industry that increases in importance with each generation of higher density integrated circuits.
Interconnect metal films typically are deposited via physical vapor deposition within a plasma chamber, and more recently via high density plasma (HDP) deposition. In both processes, a target of to-be-deposited material (e.g., the metal comprising the interconnect) is sputtered through energetic ion bombardment that dislodges atoms from the target. The dislodged atoms travel to a wafer disposed below the target and form a metal film thereon. The metal film is patterned to form the interconnect.
The use of copper in place of aluminum as the interconnect material for semiconductor devices has grown in popularity due to copper's lower resistivity. As with aluminum target manufacturers, copper target manufacturers conventionally focus on the purity of the sputtering target to reduce defect densities or to otherwise affect deposition of high quality metal films. For instance, at considerable cost copper targets presently are available with purity levels greater than 99.9999%. However, despite purity levels in excess of 99.9999%, the defect densities of copper films deposited using such high purity targets remain unacceptably high.
Accordingly, a need exists for an economical copper target that produces copper films having reduced defect densities.